Project Proposal: Stability Guidance for Small Craft Designers (Chris Barry)
1) Background:
Until relatively recently, there were only very limited criteria for the stability of craft under 65 feet, especially recreational boats. The requirements applicable to small craft were:
46 CFR 178-179 (small passenger vessels under 65 feet/100 gross tons/150 passengers): Must pass a "simplified stability test" comprising moving a weight producing a moment equivalent to either a specified shift of passenger weight to one side, or a specified wind force. Under this moment, there is a minimum required residual freeboard on the low side.
33 CFR 183 (most motor recreational boats under 20 feet): Passenger and weight capacity (posted on a mandatory label) is determined by the ability to pass tests comprising a fraction of the deadweight when evenly loaded such that the freeboard to downflood is zero, by a passenger weight shift such that the freeboard to downflood on one side is zero, and the maximum weight that can be floated in the flooded condition (by fixed foam flotation), including a shift of weight to one side. No standards are required of craft over 20 feet.
2) Recent Changes
More recently, however, ISO 12217 has been accepted for compliance to the Recreational Craft Directive (RCD) of the European Union. This has a fairly complex set of criteria based on the exposure of the craft and similar issues. The exposure criteria range from Category D (sheltered waters) to Category A (long open ocean voyages). Category A and B include "Terremolinos" type righting energy area criteria and "severe wind and wave" energy criteria, both of which involve detailed calculation of righting arms and are explicitly required to correctly assess trim on the righting arm, etc. These standards also have fairly complicated additional standards for sailing craft.
There is also growing interest in the quasi-military/police small craft market, which increasingly imposes some stability criteria as part of their procurement requirements. However, many of the builders of these craft are not experienced naval architects, either.
3) Need
As a result of this change, and based on increasing availability of computers, CAD software, and so on, (and with recent stability related accidents in small passenger craft), small craft designers are becoming increasingly interested in stability assessments beyond just single waterline hydrostatics. Unfortunately, many small craft designers have limited education in naval architecture, having either "learned by doing" without formal training or having taken mail order courses or other limited training (see, for example Westlawn and MacNaughton Group).
This means that here is an opportunity to provide training and/or material on stability issues focused on small craft designers, independent students of small craft design and others in the recreational boat industry. However, doing so practically requires more than just explaining the concepts, rather, there should be some means for a designer to actually perform at least intact stability analyses, which in turn implies the availability of basic software that could do upright hydrostatics and righting arm curves free to trim. These capabilities are included as part of a number of other packages that are primarily hull surface definition packages, but these latter may not be accessible to all students, (since they are quite expensive) and SNAME should not be in the position of endorsing just one.
There is a project in the small craft committee to develop a bulletin on small craft stability, but it would be nice if there were also a training module that included exercise problems and a minimal software package.
It may be worth figuring out if there was some way SNAME could help make something like this available, especially because this would help SNAME improve its presence in the small craft community.